The bimolecular lipid leaflet postulated as the basic structural matrix of biological membranes is widely accepted. Recent experiments have made direct studies of lipid bilayers possible. As has been demonstrated by a number of investigators, these artificially constituted bilayer lipid membranes (BLM) possess many properties resembling those of biological membranes. At the present time, a bilayer lipid membrane upon suitable modification serves as a unique model for biological membranes. The proposed project will be concerned with the biophysics of these BLM. The proposed research will be centered on the following: (1) to continue the current research program on the studies of the basic physical and electrochemistry of BLM, which should provide a more rational basis for further development; and (2) to reconstitute specific biomembrane systems with the lipid bilayer and its modifications so that simple physical, chemical, and physiological processes may be isolated and analyzed in terms of the physical and chemical properties of the constituent compounds. An important objective of this work is to obtain quantitative data on BLM, which it is hoped will provide a physical basis for an understanding of the much more complex questions of stability, ion selectivity, energy transduction, redox reactions, and transport properties in biological membranes.